The Biological Species Concept Is

The biological species concept is

A) sometimes difficult to put into practice even for present sexual organisms,and useless for asexual organisms and fossils.
B) applicable to all present life forms,but not to fossil organisms whose reproductive behavior cannot be observed.
C) easy to apply to all present sexually reproducing organisms,but harder to apply to asexual organisms and fossils.
D) applicable to all forms of life,past and present.